This is another update for this issue,
After passing the calibration and stress test and generating ddr3_timing.c file,
I tried to rebuild the u-boot-imx with the new file, and its correctly built,
but when flashing the board with UUU I got a failure, and the log output of minicom is attached.
I found many other people facing this problem with imx6 and 7, and the answers are generally to modify the imx8mm_val.h file under u-boot-imx to set the settings of DDR there too.